ExcelScript Type Definnitions

Sumurthy on GitHub wrote a file, index.d.ts, to do this. You can take a look at that file here.

The type definitions for Office Scripts are not open source. A copy of those definitions is used to generate the reference documentation. It is updated shortly after the internal definitions are updated. You can find a public copy of the .d.ts file here: https://github.com/OfficeDev/office-scripts-docs-reference/blob/main/generate-docs/script-inputs/excel.d.ts